U.S. patent number 3,952,236 [Application Number 05/490,128] was granted by the patent office on 1976-04-20 for vehicle speed regulation system.
This patent grant is currently assigned to General Electric Company. Invention is credited to James William Hoover.
United States Patent |
3,952,236 |
Hoover |
April 20, 1976 |
Vehicle speed regulation system
Abstract
A digital tachometer provides a signal proportional to output
speed which clocks a multivibrator whose "on" time is selectively
set as a function of desired speed. The output is filtered and any
deviation from one-half the peak voltage becomes the speed error
signal which is pulse width modulated to provide an error signal to
the prime mover. Proper selection of multivibrator parameters
provides for a plurality of output pulse widths which accommodate
sensitive speed regulation over a low speed range.
Inventors: |
Hoover; James William (North
East, PA) |
Assignee: |
General Electric Company (Erie,
PA)
|
Family
ID: |
23946743 |
Appl.
No.: |
05/490,128 |
Filed: |
July 19, 1974 |
Current U.S.
Class: |
318/139; 388/811;
388/915 |
Current CPC
Class: |
H02P
23/22 (20160201); Y10S 388/915 (20130101) |
Current International
Class: |
H02P
23/00 (20060101); H02P 005/16 () |
Field of
Search: |
;318/319,326,341,139 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rubinson; Gene Z.
Attorney, Agent or Firm: Bigelow; Dana F. Bernkopf; Walter
C.
Claims
What I claim as new and desire to secure by Letters Patent of the
United States is:
1. A speed regulation system for low speed vehicles comprising:
a. means for generating a first pulse train whose frequency is
proportional to actual vehicle speed;
b. a monostable multivibrator for responsively generating a second
pulse train whose repetition frequency is equal to that of said
first pulse train;
c. means comprising a potentiometer and a plurality of varied
capacitors which are capable of being individually switched into
the timing circuit of said multivibrator for varying the pulse
width of said second pulse train as a function of the desired
vehicle speed, said multivibrator having a 50% duty cycle when the
vehicle actual speed equals the vehicle desired speed;
d. means for filtering said second pulse train to obtain a d-c
signal whose amplitude varies with any difference between the
actual and desired speeds;
e. means for comparing said d-c signal with a reference signal to
obtain an error signal; and
f. means for applying said error signal to regulate the actual
vehicle speed.
2. A speed regulation system for controlling the speed of a vehicle
by comparing the actual speed with the desired speed thereof and
applying the resultant error signal to change the actual speed
comprising:
a. a digital tachometer whose output frequency is proportional to
the vehicle speed;
b. a monostable multivibrator which is triggered on in response to
said tachometer output to provide an output of the same
frequency;
c. means for selectively varying the duration of the multivibrator
output in inverse proportion to the desired vehicle speed such that
said monostable multivibrator has a 50% duty cycle when the vehicle
actual speed equals the desired speed;
d. means for filtering the monostable multivibrator output to
obtain a d-c signal whose amplitude is normal when the actual speed
equals the desired speed and deviates from normal in proportion to
the difference, if any, between actual and desired speeds;
e. means for comparing said d-c signal with a reference signal to
derive a speed error signal representative of the deviation from
normal of said d-c signal; and
f. means for applying said speed error signal to regulate the
actual speed.
3. A speed regulation system as set forth in claim 2 wherein said
output duration varying means comprises a potentiometer and a
plurality of different valued capacitors capable of being
individually switched into the timing circuit of said
multivibrator.
4. A speed regulation system as set forth in claim 2 wherein said
filtering means includes means for amplifying the average magnitude
of said second pulse train such that a change in percentage of the
actual vehicle speed will bring about a significantly greater
percentage change in said d-c signal.
5. A speed regulation system as set forth in claim 2 wherein said
comparing means is a pulse width modulator.
6. A speed regulation system as set forth in claim 5 wherein said
reference signal is a fixed frequency and amplitude sawtooth
curve.
7. A speed regulation system as set forth in claim 2 and including
means for filtering said tachometer output signal to prevent
inadvertent triggering of said multivibrator.
8. A speed regulation system as set forth in claim 2 wherein said
tachometer output is a square wave.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to motive power systems and more
particularly to systems for speed regulation of a motor in response
to a resultant error signal.
Control of power application to vehicles powered by electromotive
means is commonly accomplished by deriving an analog voltage signal
proportional to motor speed and comparing it with an analog
reference signal to produce an error signal which is in turn
applied to the regulating system to change the motor speed. This
change tends to bring the vehicle actual speed into conformance
with the vehicle desired speed. Since the accuracy of a typical
analog system decreases as the speed decreases, and since a weak
signal at low speeds results in a slot reaction, such a system is
not satisfactory for low speed operation.
An alternative method well known in the art is that of using a
digital tachometer whose output signal frequency is proportional to
velocity and whose accuracy is fixed irrespective of vehicle speed.
The signal of constant width pulses is filtered and the resulting
d-c signal is compared with a reference voltage to generate an
error signal to the motor. Since the width of the pulses are
constant throughout the speed range of the vehicle and since it is
necessary to use narrow pulses to accommodate high frequencies,
then at low frequencies the accuracy is necessarily depreciated. In
certain instances this may be of great concern, as for example,
when maintaining creep control at speeds of approximately one-half
mile per hour during the loading of coal into a vehicle.
It is therefore an object of this invention to provide a speed
regulation system for vehicles operating at low speed ranges.
Another object of this invention is the provision for a speed
regulation system which is accurate at very low speeds and is
capable of effective speed regulation at higher speeds.
Yet another object of this invention is the provision for a speed
regulation system which is equally sensitive and accurate over a
range of low speeds.
Still another object of this invention is the provision for a speed
regulation system which is economical to manufacture and effective
in use.
These objects and other features and advantages become more readily
apparent upon reference to the following description when taken in
conjunction with the appended drawings.
SUMMARY OF THE INVENTION
Briefly, in accordance with one aspect of the invention, a
retriggerable monostable multivibrator is triggered on in response
to a square wave signal representative of vehicle speed as sensed
by a digital tachometer. The multivibrator stays on for a period
determined by the selected speed of the vehicle and the output of
the multivibrator is thus a square wave having constant pulse
widths as determined by the desired speed setting and having a
frequency equal to that of the tachometer input signal. The square
wave output is then actively filtered to obtain a d-c signal having
an amplitude which depends on the difference, if any, between the
sensed speed of the vehicle and the selected speed thereof. The d-c
signal which is then amplified and pulse width modulated to obtain
a square wave control signal which is applied to the excitation
system of the the vehicle propulsion equipment.
In accordance with another aspect of the invention the d-c signal
is amplified such that when a balanced speed condition exists the
d-c signal is at its midpoint and the resulting control signal is
at a 50% duty cycle.
By another aspect of this invention different capacitive timing
components of the multivibrator are switched in at various speed
stages so as to obtain wider pulses at lower speeds, and allow for
the potentiometer to be adjusted over its full range within each
one of the capacitor ranges.
Yet another aspect of this invention provides for a rate-of-change
limit during start-up when the vehicle is stopped and a large error
signal immediately exists.
In the drawings as hereinafter described, a preferred embodiment is
depicted; however, various other modifications and alternate
constructions can be made thereto without departing from the true
spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of the preferred embodiment of
the invention.
FIG. 2 is a graphic illustration of various waveforms that are
generated within the system of the preferred embodiment.
FIG. 3 is a schematic diagram of the circuitry of the preferred
embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1 a closed loop system is shown in accordance
with the present invention including a prime mover 11 connected to
drive a propulsion drive system 12, as for example, in a diesel
electric locomotive where a diesel engine drives electric
propulsion motors to propel the vehicle. The actual speed of the
vehicle is sensed by an axle mounted tachometer 13 of the digital
type, and the output signal (see waveform of FIG. 2(a)) whose
frequency is proportional to speed is transmitted to clock a
monostable or "one-shot" multivibrator 14 whose "on" time is set as
a function of the desired speed by proper selections in the
reference circuit 16. When the actual speed as sensed by the
tachometer 13 is equal to the desired speed as set by the reference
circuit, then the output signal F of the multivibrator is a 50%
duty cycle wave as is shown in FIG. 2(b). When the frequency of the
tachometer output signal is less than the desired frequency as is
shown in FIG. 2(c), then the output signal of the multivibrator is
at less than 50% duty cycle as is seen in the waveform of FIG.
2(d). Conversely, if the vehicle speed is higher than that called
for the duty cycle of the multivibrator output would be greater
than 50%. Any variance one way or the other from the 50% duty cycle
represents an error signal which must be applied to the system.
The square wave output signal F from the multivibrator passes to an
averaging circuit 17, where it is converted into a d-c signal V
whose amplitude is normal (i.e., at mid scale when the actual
velocity equals the desired velocity and varies from normal as the
actual velocity changes from desired. This signal passes to the
amplifier 18 which sets the gain of the system and limits the rate
of application of power, and the amplified signal passes to a
comparator 19 where it is compared with a reference signal 21 to
derive an error signal. The comparator 19 comprises a pulse width
modulator which compares the d-c signal with a triangular waveshape
of fixed amplitude and frequency as shown in FIG. 2(e). When a
balanced speed has been attained, the d-c signal of waveform 2(e)
is midway between the triangular wave peaks and the output duty
cycle (FIG. 2(f)) is at 50% to provide 1/2 maximum power.
Assuming now that a disturbance occurs so as to cause the vehicle
speed to decrease and the signals of waveforms 2(c) and 2(d) to be
produced. Since the duty cycle of waveform 2(d) is less than 50%,
the d-c level of the signal V from the averaging circuit 17 becomes
lower than normal, and when introduced into the comparator 19 (see
FIG. 2(g)) the resulting error signal duty cycle (FIG. 2(h))
becomes greater so as to apply more power to the drive system and
thereby increase the vehicle speed. Conversely, if the vehicle
speed reaches a level above the desired speed then the resulting
waveforms will be as in 2(j) and 2(k) to reduce the applied power
and speed of the vehicle.
Referring now to FIG. 3 the circuitry of the invention is shown in
detail and includes the prime mover 11, tachometer 13,
retriggerable monostable multivibrator 14, reference circuitry 16,
averaging circuit 17, amplifier 18, comparator 19 and reference
generator 21. The tachometer 13 is driven by the prime mover 11 to
provide a square wave signal to the base of an NPN transistor 25 by
way of a serially connected diode 22 and resistances 23 and 26. A
capacitor 27 connected between the junction of the two resistances
and ground completes a filter network for the removal of noise
which could cause the inadvertent triggering of the monostable
multivibrator 14. A resistance 28 is connected across the capacitor
to provide a path for the transistor base leakage current. The
collector of the transistor 25 is connected through resistor 29 to
a constant potential source and to the input of an inverting
amplifier 31. The transistor emitter is connected to ground.
The inverted output from amplifier 31 passes to the B terminal of
the monostable multivibrator 14 to trigger it on when the signal
goes negative. It stays on until the various timing components of
the reference circuit 16 allow it to turn off. The timing
components comprise a fixed resistance 32 and a potentiometer P in
series between the multivibrator and a fixed voltage source.
Connectable across the terminals are the capacitors 33, 34 and 36,
with the desired capacitance level being selected by a switch S to
accommodate a particular speed range. In other words the pulse
width of the multivibrator output is selectively adjusted to one of
three different levels by selection of the proper capacitance. For
lower speeds the pulse width is maximized to enhance the system
accuracy, whereas at higher speeds the pulse width is narrowed to
accommodate the high frequency pulse train. Typically the three
capacitors accommodate the speed ranges 1/4 - 1 mph, 3/4 - 3 mph
and 2 - 8 mph, respectively, and the potentiometer is adjusted
continuously to set the desired speed within the 0 - 8 mph
range.
At the power supply terminals a capacitance 36 is provided between
the voltage source and ground for noise suppression. The
multivibrator operates in a conventional manner as described in
Pulse, Digital, and Switching Waveforms, Millman and Taub, McGraw
Hill Inc., 1965.
At the output terminal Q of the multivibrator there is thus
produced a square wave pulse train whose repetition frequency is
equal to that of the tachometer input signal and whose pulse width
is fixed by the timing components. This output is inverted by an
inverting amplifier 37 (both gates 31 and 37 are installed for the
purpose of isolating the multivibrator) and passed through a diode
38 to the averaging circuit 17 where it is converted to a d-c
signal whose amplitude varies directly with speed differential
(i.e., with the amount by which the actual velocity of the vehicle
differs from a balanced speed condition wherein its just equals the
desired velocity) and is at mid scale when in a balanced speed
condition. The averaging circuit is simply an active filter wherein
the input goes to the base of an NPN transistor 39 whose collector
is connected to a positive source through a resistance 41, and to
the input terminal of an amplifier 42 through resistances 43 and
44. The emitter of the transistor 39 is connected to ground and a
resistance 46 is connected between the transistor base and ground.
The amplifier 42 has feedback loops with a capacitor 47 and a
resistance 48. A capacitor 49 is connected between ground and the
junction of resistances 43 and 44 and a resistor 51 is placed
between the amplifier and ground.
Line 52 transmits the d-c signal from the filter output to the
amplifier 18 which sets the gain of the system and controls the
initial rate of change. An operational amplifier 53 has an input
resistor 54, ground resistor 56 and feedback resistor 57 and
capacitor 58. A fixed bias voltage is provided to set the system at
a 50% duty cycle and to provide the desired sensitivity of
operation. For example, at a balanced speed condition the output of
the amplifier 18 is at mid range, but the occurrence of a change of
speed 1% will cause a change of the d-c voltage signal of
approximately 8 - 10% and thereby create an immediate response to
reduce the error signal. During start-up the initial rate of change
is limited by a capacitor 59 and diode 61 connected around the
operational amplifier 53 so as to allow the output to change slowly
for positive going signals but permit rapid change for negative
outputs. This limits the rate of application of initial power
wherein the train is stopped and a large error signal immediately
exists on start-up. A switch S, and associated resistance 62 is
provided to short the amplifier when the switch is closed so as to
present a zero output from the amplifier and thereby inactivate the
system.
During active operation the amplifier d-c signal goes to the
comparator 19 where it is compared with a triangular reference wave
from the reference signal generator 21. This generator comprises a
pair of operative amplifiers 63 and 64 with the output of the first
63 going to the input of the second 64 through a capacitor 66 and
resistance 67. Amplifier 63 has in its feedback network a feedback
resistor 68 in one loop and the resistors 69 and 71 along with a
timing capacitor 72 in the other loop so as to comprise a square
wave oscillator whose output is capacitively coupled to the
integrating circuit 64 having feedback resistor 73, feedback
capacitor 74, and ground resistor 76. A negative bias is applied
through resistor 77. The resultant waveform is a sawtooth signal
which is compared with the d-c signal in the comparator 19 to
obtain a square wave signal as shown in FIGS. 2(e) and 2(f). The
square wave signal is applied through resistor 78 to the base of a
transistor 79 whose emitter is tied to ground with a clamping diode
81 back to the base to prevent any reverse voltage condition from
exceeding a safe limit. The transistor collector is connected
through resistor 82 to the exciter driver where the square wave
signal is applied to regulate the excitation level of the generator
and hence the power to the motor.
In operation assume that the vehicle is initially at a standstill
and that the potentiometer P is set to represent a desired speed. A
speed differential will exist but an error signal will not be
immediately applied because of the rate limiting components of the
amplifier 18. After a delay period an error signal will be
generated, and as long as the vehicle speed signal as sensed by the
tachometer is less than the desired speed as set by the
potentiometer, the multivibrator output will be at less than 50%
duty cycle, the d-c signal will be below its mid point, and the
square wave control signal to the exciter will be at greater than
50% duty cycle. The reaching of a balanced speed condition will
result in a 50% duty cycle from the multivibrator and to the
exciter, and an overspeed condition will result in a waveform at
greater than 50% duty cycle from the multivibrator and less than
50% duty cycle to the exciter. If after the potentiometer has been
adjusted through its complete range, a greater speed is desired,
then the switch S is moved to bring in another capacitance level so
as to enable the further widening of the multivibrator output
pulses. The potentiometer P may then be adjusted through its
complete range until the third capacitive stage is brought in for a
still higher speed range. In this way accurate and sensitive speed
regulation is maintained throughout a range of low speeds.
* * * * *